I still need to try some of the Evangelion spin offs. I've just have had way too much anime too watch lately.
Read Evangelion: Campus Apocolypse. That is awesome if you want the same Evangelion type suspense, combined characters but a new universe. It's pretty good, though far from being completed if I remember all right.
Angelic Days is very good.
Another great one is, 'Neon Genesis Evangelion: The Shinji Ikari Raising Project". But I'm biased that's why I think it's good.
But in all actuality the best spin off I've read recently, though at times it's really lacking in the continuity of the characters, is Evangelion: Re-Take. It's a doujinshi, but only in the sense that it's fan made. There is some ero in it, but it's not randomly
thrown in for sex appeal. there are always some sort of build ups to it. It's a very good spin off and actually is a lot of fun to read. Not your typical type Evangelion story, but definitely worth the read. It's about, what if Shinji got a second chance to
redo the last several weeks before End of Eva.